Small amplitude rapid and slow eye movements occur continuously when a human subject is instructed to look only at a small target. These fixation eye movements are so small that they cannot be examined by the usual routine methods and require extremely sensitive eyetracking instruments for accurate detection. It is possible that fixation movements require precise control from supranuclear oculomotor structures of the brain to maintain their configuration and that human diseases which impair this supranuclear control produce specific qualitative and/or quantitative changes in fixation eye movements. The major objective of the present proposal is to test this possibility by measuring fixation eye movements in patients with selected neuroanatomic or oculomotor disorders and in patients with multiple sclerosis and then comparing the findings to similar measurements in control subjects. The research plan may determine the following: 1. If disorders of the areas of the brain that provide the supranuclear control of large amplitude eye movements produce specific alterations in fixation movements. 2. If disorders of fixation movements, which are undetectable by routine clinical examination, can be of diagnostic importance in patients with neurological disorders such as multiple sclerosis. 3. If the quantification of fixation provides an accurate method for determining when these eye movements are normal or abnormal, and when examined serially provides a monitor of the course of the neurological disorder and attempted treatment regimens. 4. If large amplitude pathological fixation instability in patients with neuroophthalmological disorders evolve from normal fixation movements.